Compression experiments

Lyzenga, G.A., and Ahrens, T.J. (1979), Multi wavelength Optical Pyrometer for Shock Compression Experiments, Rev. Sci. Instrum. 50, 1421-1424. 

Jones, O.E. and Graham, R.A., Shear Strength Effects on Phase Transition Pressures Determined from Shock Compression Experiments, in Accurate Characterization of the High Pressure Environment (edited by Lloyd, E.C., National Bureau of Standards Special Publication 326, US Government Printing Office, Washington, DC, 1971, pp. 229-242. 

After all the previous statements, it would seem very difficult to select a piston. speed. For someone without direct experience, the following guidelines can be used as a starting point. Actual gas compressing experience should be solicited when a new compressor for the same gas is being eonsidered. These values will apply to the industrial process type of compressor with a double-acting cylinder construction. For horizontal compressors with lubricated cylinders, use 700 feet per minute (fpm) and for nonlubricated cylinders use 600 fpin. For vertical compressors with lubricated cylinders, use 800 fpm and for nonlubricated cylinders use 700 fpm. 

The work of the present section shows that shock-compression experiments provide an effective method for determination of higher-order elastic properties and that, by the same token, the effects of nonlinear elastic response should generally be taken into account in investigations of shock compression (see, e.g., Asay et al. [72A02]). Fourth-order contributions are readily apparent, but few coefficients have been accurately measured. 

Perhaps the most widely misunderstood aspect of gauge development is the role of the controlled shock-compression experiment in the development process. It is often stated that the gauges are being calibrated. In fact, it is not possible to calibrate a gauge that must be used over the wide range of conditions and over the wide range of wave profiles encountered and is destroyed in use. Only in special cases of shocks to fixed conditions is the response measured for a gauge in controlled experiments directly a suitable calibration. Even in the direct shock experiment, the controlled shock-compression experiment serves as a shock calibration only if the reproducibility of materials in the sensor is evaluated quantitatively and a persistent reproducible materials source is available. 

To further clarify the role of magnetic effects on compressibility, a shock compression experiment was performed on an fee 28.5-at. % Ni sample whose initial temperature was raised to 130°C. As is shown in Table 5.1, the compressibility was found to decrease to a value consistent with the nonmagnetic compressibility. Thus, the sharp change in compressibility, the critical values for the transition, and the magnitudes of the compressibility under the various conditions give a clear demonstration that a second-order magnetic transition has been observed, and we will proceed with a quantitative analysis of the transition. 

The shock-compression induced structural phase transformation in iron from the low pressure bcc phase to the high pressure hep phase is one of the most visible problems studied in shock-compression science, and its discovery was responsible for widespread recognition of the capabilities of the high pressure shock-compression experiment. The properties of many shock-induced phase transitions are summarized in Duvall and Graham [77D01]. 

Determination of cross-link density from compression experiments is perhaps the most effective means of determining cross-link density as long as samples of the appropriate geometry can be prepared. When a hydrogel is subjected to an external force, it undergoes elastic deformation which can be related to the effective cross-link density of the network [63,99], Here the measurements made to extract cross-link density from polymer deformation are briefly discussed. 

Figure 19. Pressure shift of the absorption edge of benzene (circles) and furan (squares) during room-temperature compression experiments. Empty symbols correspond to the value of the absorption edge measured on the reacted material on releasing pressure.

Compression in a Roots pump is performed by way of external compression and is termed as isochoric compression. Experience shows that the following equation holds approximately ... 

It has long been known that acetylene explodes under the influence of compression. Experiments by Rimarski and Metz [99] showed that at a temperature below 500°C acetylene does not explode if the pressure is lower than 3 kg/cm2. An explosion may occur at 510°C under a pressure of 2.05 kg/cm2. At room temperature acetylene may explode provided it is compressed adiabatically with a pressure of 170 kg/cm2. 

All experiments using lipid membranes employed equal weight ratios of the phospholipid or oxidized phospholipid, and one of the steroids. For the trough experiments, 2 mg of phospholipid and 2 mg of steroid were dissolved In a total of 5 ml of solvent. Hexane was used as the solvent In most Instances, but sma1 1 quantities of chloroform were necessary as a secondary solvent for complete dissolution of the steroid dlol and trlol species. Approximately 0.1 ml of solution was slowly spread on the aqueous sub-phase (consisting of pure water or 0.1 M KC1) In the trough, and the solvent was allowed to completely evaporate before compression experiments were Initiated. Compression was performed slowly In all cases to allow surface equilibration and each sample solution was Investigated at least four times to ensure reproducibility. 

The cubic y-modification has been recently observed under a pressure of 15 GPa and temperatures above 2000 K by the laser heating technique in a diamond cell [23] and in shock-wave compression experiments with pressures >33 GPa at 1800 K and >50 GPa at 2400 K [29]. This modification is often designated as the c-modification in the literature in analogy to the cubic boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms are octahedrally coordinated by six nitrogen atoms, one silicon atom is coordinated tetrahedrally by four nitrogen atoms (Fig. 3c). The atomic coordinates for the cubic modification are given in Table 2. From calculations it is shown that this structure should have a high hardness similar to that of diamond and c-BN [23]. 

In this study, uniaxial confined swelling and compression experiments were performed on a hydrogel that mimics the behaviour of biological tissues. The deformation of the sample and the electrical potential difference over the sample, caused by varying mechanical and chemical loads, were measured successfully. 

In articular cartilage, streaming potentials have been demonstrated by permeation experiments and confined compression experiments [2, 4, 7, 9, 14, 15], In the permeation experiments, a hydrostatic pressure gradient is applied across the sample. The pressure generates a fluid flow and a streaming potential that can be measured [9, 15]. 

Streaming potentials are also generated by deformation of the tissue. Lee et al. [14] and Frank et al. [4] measured streaming potentials generated by oscillatory compression experiments. Chen et al. [2] measured streaming potentials in confined compression experiments. In these experiments, bovine cartilage discs were subjected to step changes of the compressive stress. 

The goal of this study is the measurement of the electrical potential gradient caused by mechanical and chemical loads in a confined swelling and compression experiment. 

The samples were put in an uniaxial swelling and compression testing device (figure 1). In a uniaxial confined swelling and compression experiment, a cylindrical sample was enclosed in an impermeable confining ring made out of Athlon (Trespa International B.V., The Netherlands). This was done in... 

Figure 2. Experimental results for 2 confined swelling and compression experiments performed on hydrogel. The boundary conditions are given in the corresponding top figures.

Also in other confined compression experiments, a streaming potential was measured when a mechanical load was applied [2], This streaming potential is characterised by an electrokinetic coefficient ke ... 

In our confined swelling and compression experiment, we also applied a mechanical load to the sample (t = 12.5 h). We measured a streaming potential A = 0.85 0.65 mV. The change in the mechanical load A a equals -0.117 MPa. Thus, the value for the electrokinetic coefficient is —7.3 5.6 mV MPa-1. This was in the same range as measured for bovine cartilage. 

Figure 5 Compression experiment. Particle compressed by force F between surfaces separated by the distance 2fj.

Kim (82) estimated PED from compressive experiments on molded disks of a number of materials, as shown in Fig. 5.17. High modulus, yielding, amorphous polymers such as PS dissipate a large amount of mechanical energy, compared to lower modulus, polycrystalline polymers, as shown again in Fig. 5.17. Iso-PED and corresponding iso-ATadiab contours can be obtained from a number of cylindrical specimens compressed to various strains at various initial temperatures, as shown in Fig. 5.18(a) and 5.18(b). From such plots, the expected ATadiab from one or more successive E deformations can be obtained, as shown in Fig. 5.19, for PS compressed to successive eo = 1 deformations. 

Viscosity has been replaced by a generalized form of plastic deformation controlled by a yield stress ty, which may be determined by compression experiments. Compare with Eq. (20-48). The critical shear rate describing complete granule rupture defines St, whereas the onset of deformation and the beginning of granule breakdown defines an additional critical value St. ... 

We summarize the results of these expansion and compression experiments in Table 10.3. The most important conclusion that can be drawn from these results can be stated as follows Only when the expansion and compression are both done reversibly (by an infinite number of steps) is the universe the same after the cyclic process (the expansion and the subsequent compression of the gas back to its original state). That is, only for the reversible processes is the heat absorbed during expansion exactly equal to the heat released during compression. In all the processes carried out using a finite number of steps, more heat is released into the surroundings than is absorbed in the comparable expansion (same number of steps). 

TABLE 10.3 Summary of the Isothermal Expansion and Compression Experiments... 

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